Downing Street has claimed that the Home Office’s controversial “go home”
immigration campaign is “already working” and suggested the scheme could be
rolled out across the country.

According to David Cameron’s spokesman there has been a “great deal of interest” from illegal immigrants voluntarily calling a Government helpline and asking how to leave the country.

However, Downing Street later indicated that the Home Office has not actually provided any statistics that prove the scheme is working and that officials have merely told their Number 10 counterparts that it has been a success.

It came as Downing Street slapped down Vince Cable, the Business Secretary, who yesterday described the campaign telling illegal immigrants to “go home or face arrest” as “stupid and offensive”.

The strategy has seen vans displaying posters targeted at illegal immigrants driving around six London boroughs.

Asked whether the Prime Minister agreed with Mr Cable’s view that the posters are offensive, Mr Cameron’s spokesman said: “No is the short answer. This pilot is about targeting people who are here illegally and giving the opportunity to leave the country voluntarily rather than be arrested, detained and removed and we know that voluntary returns are the most cost effective way of removing illegal immigrants.”

He added: “If you talk to the Home Office they can tell you that they’ve had a great deal of interest and they are looking at seeing which inquiries they can take forward.”

A Home Office source later said that the vans pilot had only ended on Sunday and that statistics on the scheme may not yet have been compiled.

Asked if the pilot would be extended nationwide , the Prime Minister's spokesman said: "The Home Office has said this is already working. Clearly, we will want to look at that in more detail and see how we take this forward."

The Lib Dems and community groups claim the posters are divisive and heighten racial tensions. Nigel Farage, the leader of Ukip, has also voiced concern.

Mr Cable said it was already difficult to be an immigrant in Britain and made clear that the Lib Dems had not sanctioned the Home Office’s “pilot” scheme.

He claimed that the Conservatives were “obsessing” about the total level of immigration, which was leading them to make poor policy decisions.

However, Downing Street insisted the pilot had been signed off by “the Home Office team”, indicating that it has had support from Jeremy Browne, a Lib Dem minister in the department.